Evolution of male life histories and age-dependent sexual signals under female choice

Strategic models have predicted that males could benefit from age-dependent sexual advertisement following evolution of increased lifespan. Dynamical considerations may play a crucial role in the origin of age-dependent sexual signals, despite strategic advantages in populations with established signals and preferences. I investigated the problem that rare trait-bearing males may suffer low viability due to small young-age signals, restricting the favorable conditions for age-dependent trait evolution. I also ask when age-dependence will prevail during trait evolution if males bearing age-dependent traits co-occur with males carrying age-independent traits. I used numerical simulations to analyze the evolution of an age-structured haploid population with no genetic drift. Age-dependence limits the evolution of male traits to cases of relatively weak selection against the trait, but the trait fixes at smaller sizes when age-dependent than when age-independent. When mode of expression (age-dependence versus age-independence) evolved along with the trait, age-independence prevailed over much of parameter space, although mode of expression remained polymorphic at small trait sizes under weak selection. The ubiquity of age-dependent traits in nature shows that many species’ life-histories satisfy the conditions for age-dependent trait evolution. My results suggest that high adult male survival facilitates sexual selection by favoring the evolution of age-dependent sexual signals under fairly broad conditions.